An engine usually includes an exhaust gas recirculation (EGR) mechanism for reducing the harmful components contained in the exhaust gas by recirculating the exhaust gas into the gas intake system.
That is, as is shown in FIG. 6, in an engine 202, an intake pipe 206 forming an intake passage 204 and an exhaust pipe 210 forming an exhaust passage 208 are disposed in a connected relation. An EGR valve 212 is attached to the intake pipe 206. Disposed between the EGR valve 212 and the exhaust pipe 210 is an EGR pipe 216 forming an EGR passage 214.
In an intermediate portion of the EGR pipe 216, an EGR switch-over valve (VSV) 218 is disposed. This EGR switch-over valve 218 is operation-controlled by a control means (ECU) 220.
Input into the control means 220 are data of the driving state of the engine 202 such as cooling water temperature, intake pipe absolute pressure PM, intake-air temperature, throttle opening degree, number of engine revolution (engine rotational speed), etc.
The control means 220 is connected to a crank angle sensor 222 mounted on the engine 202 and adapted to detect the crank angle, and is also connected with an ignition mechanism (ignitor) 224 for the engine 202. This ignition mechanism 224 is of an electronic spark advance (ESA) type.
In FIG. 6, the controlling of the EGR rate to the intake system is performed by an on/off operation of the EGR valve 212. This being the case, the ignition timing at this time is either held constant whether the recirculation of exhaust gas is effected or not, or adjusted in two stages depending on whether the recirculation of exhaust gas is effected or not.
On the other hand, in an ignition timing control operation of an ignition mechanism of a distributor type instead of the ignition mechanism of an electronic spark advance type, the ignition timing is held constant whether the recirculation of exhaust gas is effected or not.
One such ignition timing control apparatus is disclosed, for example, in Japanese Patent Early Laid-open Publication No. Sho 57-179370 and Japanese Utility Model Early Laid-open Publication No. Sho 61-66667. One, which is described in Japanese Patent Early Laid-open Publication No. Sho 57-179370, is designed such that if, at the time a non-operating state of the EGR valve is detected, the engine speed and the value of a signal representing the amount of air intaken are within the ranges of the amount of intaken air and the engine speed on level ground, then the ignition timing is optimally corrected in order to prevent the occurrence of knocking of the engine also on a high land.
Another apparatus, which is described in Japanese Utility Model Early Laid-open Publication No. Sho 61-66667, is designed such that the ignition timing is corrected in accordance with EGR based on the change in the rate of EGR.
There is conventionally an inconvenience in that, since the control means does not have a single kind of ignition timing map, the ignition timing at the time that recirculation of exhaust gas is not effected is excessively spark advanced, thus exerting adverse affects on drivability, emission, etc.
Also, because of the above-mentioned reason, the exhaust gas recirculation mechanism cannot be turned on/off positively depending on driving conditions of the engine and, therefore, improvement was demanded.
Further, even in case the control means is provided with two kinds of ignition timing maps for performing an on/off operation for the exhaust gas recirculation mechanism, there is an inconvenience in that an attempt is made to control the rate of EGR, and the ignition timing is excessively spark advanced or excessively spark halted because the required ignition timing is uselessly changed due to difference in the rate of EGR.
Therefore, an object of the present invention is to provide an ignition timing control apparatus for an engine, in which a duty-controlled EGR rate regulating solenoid valve is disposed midway along an EGR passage intercommunicating an exhaust passage and an intake passage, and by adjusting the ignition timing in accordance with a duty rate which controls the EGR rate regulating solenoid valve, the EGR rate is changed in a non-stage manner and the ignition timing is optimally adjusted in accordance with this EGR rate, thereby enhancing the drivability and obtaining the most appropriate exhaust emission.
In an attempt to achieve the above object, in an engine including an exhaust gas recirculation mechanism for recirculating a part of the exhaust air into the gas intake system, the present invention is characterized in
a duty-controlled EGR rate regulating solenoid valve is disposed midway along an EGR passage intercommunicating the exhaust passage and the intake passage, and means for controlling the activation of the engine ignition mechanism is provided in order to adjust the ignition timing in accordance with a duty rate which is applied to said EGR rate regulating solenoid valve.
According to the constitution of the present invention, since the control means actuates the ignition mechanism in accordance with the duty rate applied to the EGR rate regulating solenoid valve to adjust the ignition timing, the ignition timing can be optimally set when the EGR rate is changed in a non-stage manner and by this, the EGR rate can be positively controlled to enhance the drivability and to obtain the most appropriate exhaust emission.